Statistics from the United States demonstrate the importance of passive safety in vehicle rollovers. In 1998, half of all single vehicle fatalities were attributed to a rollover. Vehicle rollovers account for approximately 20% of all vehicular accidents.
Traditional rollover detection systems consider the rolling motion and accelerations in x, y, and z directions of the vehicle. Reliable detection of a vehicle rollover is possible on this basis, but a decision as to whether a rollover is occurring is made only at a late point in time in the rollover. In certain cases of vehicle rollover preceded by an electronic stability maneuver, the occupant experiences a high transverse acceleration. Such maneuvers may result in a type of rollover known as a soil-trip rollover. In this regard, there is still potential for future occupant protection systems with regard to deployment behavior.
Conventional methods are based on analysis of a yaw rate sensor, for example, and two acceleration sensors that are integrated into a central airbag control unit. The yaw rate sensor ascertains the rotational speed about the longitudinal axis of the vehicle according to the gyroscope principle, and acceleration sensors additionally measure the vehicle acceleration in both the transverse and the vertical directions. The yaw rate is then analyzed in the main algorithm. Using the measured values from the acceleration sensors, it is possible to ascertain the type of rollover, but in addition, these values are used for a plausibility check. If the yaw rate algorithm detects a rollover, the safety devices are activated only if there is a simultaneous release by the plausibility check.
In another conventional method, a timely deployment decision in the case of a rollover having a high transverse acceleration is made possible by including a float angle and the lateral speed of the vehicle. In a conventional method for expanded rollover detection, an estimate of the lateral speed is made on the basis of a yaw rate and the vehicle speed in the longitudinal direction, taking into account the transverse acceleration, and this lateral speed represents a measure of the rollover probability of the vehicle in the case of lateral drift into the median strip. The float angle, as it is called, is used to determine the lateral speed.
In general, early deployment decisions for occupant protection devices, e.g., window airbags, are necessary and appropriate for a rollover. In addition to the lateral vehicle speed, the roll angle at the start of such a rollover event therefore constitutes an important quantity for predicting the rollover event. In cases of deployment decisions for irreversible occupant protection devices, the roll angle in particular plays an important role, so that the knowledge of the roll angle may be used to make a deployment decision accordingly earlier.
In the case of the conventional technical approaches, the signals of the transverse and vertical acceleration sensors are used only to detect the type of rollover and to perform a plausibility check on the roll rate measured using a roll rate sensor and the roll angle is calculated therefrom. For example, International Application WO 2001/044020 describes a method for determining the absolute angle of rotation of an object rotating about a horizontal axis, the absolute angle of rotation of the vehicle being able to be ascertained in a limited interval via a vertical acceleration sensor and a roll rate sensor.
With the conventional methods, the roll angle is not estimated independently of a roll rate sensor, which should ideally yield an independent estimate of the angle by integrating the roll rate over time. In addition, it is very difficult to determine very small angles (<5°) due to sensor noise of the roll rate sensor.